(1) Field of the Invention
The present invention relates to driving circuits for lighting devices. More particularly, the present invention relates to driving circuits, sometimes referred to as ballast circuits, that handle not only high impedance lighting devices, such as halogen lamps, but also low impedance lighting devices, such as light emitting diodes (LED). Specifically, the present invention provides driving circuits that operate and excite devices for light emissions therefrom regardless of the impedance ratings thereof.
(2) Description of the Prior Art
In various applications, such as in the automotive field, driving circuits are employed that receive a d.c. voltage which is converted to an a.c. voltage and utilized to excite lighting devices. The lighting devices are commonly connected to the output stage of the driver circuit by means of an E-Transformer, known in the art. These driving circuits operate well for exciting high impedance lighting devices, such as halogen lamps, but are plagued by problems when the lighting device is a low impedance device, such as a light emitting diode (LED). The inability to provide a driving circuit that employs an E-Transformer in its output stage that can successfully operate lighting devices having low or high impedance ratings places an undue restriction on the automotive industry. Accordingly, it is desired to provide a driving circuit having an E-Transformer in its output stage that is used to successfully operate lighting devices having a full range of impedance ratings.